1. Field of the Invention
The present invention relates to curable epoxy resin compositions and a process for the production thereof.
This application is a continuation of the National Stage of International Application No. PCT/JP02/11395, filed on Oct. 31, 2002, the content of which is incorporated herein by reference.
Priority is claimed on Japanese Patent Application No. 2001-334477, filed Oct. 31, 2001, the content of which is incorporated herein by reference.
2. Description of Related Art
Due to their high levels of reactivity and superior resin characteristics, epoxy resins are used in a wide variety of fields, including laminated sheets, sealing materials, paints, anticorrosion primers, adhesive materials, molded materials, and construction materials. In recent years, problems such as heat generation associated with the shift to higher frequency electronic equipment, and the need to adapt to lead-free solder have meant that the development of curable epoxy resin compositions capable of producing heat resistant cured products with high glass transition temperatures that can be used in laminates, adhesives, paints and binders and the like has become a priority.
One representative example of a process for improving the heat resistance of a cured product of an epoxy resin is a process in which a boron compound is added to a mixed system of an epoxy resin and an amine based curing agent (see Japanese Unexamined Patent Application, First Publication No. Hei 5-59261). However, simply adding a boron compound to a mixed system of an epoxy resin and an amine based curing agent in this manner does not significantly increase the glass transition temperature of the cured product, and the heat resistance of the cured product remains inadequate. Furthermore, because aggregates of the boron compound are dispersed unevenly through the product, the cured product tends to be brittle.
Furthermore, in another known process for improving the storage stability of a curable epoxy resin composition, a gel product produced by reacting a polyamine with an epoxy resin is subjected to a mechanical crushing treatment to produce a powder of ultra-fine particles, the surface of these ultra-fine particles are coated with a borate ester to form a latent curing agent, and this latent curing agent is then added to an epoxy resin (see Japanese Unexamined Patent Application, First Publication No. Hei 6-73156). However, even if this latent curing agent is in the form of a powder of ultra-fine particles, because the agent is still essentially a gel cured product, it cannot be uniformly compatible with the epoxy resin. In addition, the borate ester coated onto the surface of the powder aggregates markedly during curing of the epoxy resin. As a result, the curing performance of the epoxy resin deteriorates, and the glass transition temperature of the obtained cured product does not increase significantly, meaning the glass transition temperature of the cured product does not increase significantly, and the heat resistance of the cured product is still inadequate. Furthermore, the marked aggregation of the borate ester causes the cured product to become brittle.